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A very hungry, invasive caterpillar is turning trees into full-course meals in Michigan

While the spongy moths appear every spring, Terry and Chris Bennett say this season sets a new standard.
Spongy Moth Caterpillar
Posted at 8:06 AM, Jun 10, 2024

They're nature's "literal" party poopers, according to the Michigan Department of Natural Resources. And this spring, the spongy moth has reared its hungry caterpillar head, chomping through the leaves of hardwood trees on southwest side of the state.

The invasive species prefers the trunks of oak trees, where caterpillars hatch from fuzzy, tan-colored egg clusters in April and munch and munch some more through late June, raining down BB-sized droppings (referred to as frass) as they dine.

On their rural property in western Michigan, Terry and Chris Bennett can "hardly see the trees for the worms crawling on them."

"They never slowed down," Terry Bennett said. "They kept getting worse and worse and worse."

While the very hungry caterpillars appear every spring, this season sets a new standard, they say.

"[They're] smushed all over the road," Chris Bennett said. "Changes the color of the road. They're that bad."

Spongy Moth Caterpillar

The Bennetts scrape egg clusters and crush caterpillars when they see them on walks in the woods, but these efforts don't "do a bit of good" against the current population, seemingly crowding every hardwood tree in sight and leaving them vulnerable to disease.

"Pretty sad when you can look up into the trees and see that there's very few leaves," Terry said.

Meanwhile, the Michigan Department of Natural Resources says spongy moth populations are actually dropping statewide, citing sharp declines in defoliation. In 2023, it recorded 386,000 acres of spongy moth-related damage through aerial surveys, compared to the 1.3 million acres of spongy moth-related damage from 2021.

While the department predicted continued population decline in 2024, it said "some defoliation" was still likely in southwest Michigan, including where the Bennetts live.

Spongy Moth Caterpillars

"Remember that spongy moth outbreaks are cyclical and will collapse in one to three years, even without intervention," the DNR said on its website.

On the farm, though, the Bennetts are still waiting for the bug to break.

"We wonder what's going to happen," Terry said. "What the state or county is going to do to try to control these things."

Spongy Moth Caterpillars

The pesticide Btk (Bacillus thuringiensis var. kurstaki), which does not adversely affect humans or animals, can be used to target spongy moth caterpillars.

Begone, bugs!

Here are a few tips for how to prevent the spread of the spongy moth:

  • Inspect decks, outdoor furniture, fences and trees
  • Scrape egg masses into a bucket of soapy water or burn or bury them
  • Use a broom to sweep caterpillars into a bucket of soapy water, letting them soak overnight
  • Make a tree trunk trap: Cut a band of burlap and wrap it around the trunk. Tie a string around the center of the band and make a two-layered skirt around the trunk. When caterpillars climb the trees, they will get caught in the band. Duct tape will also work as an alternative to burlap.
Spongy Moth Egg Masses

This story was originally published by Sam Landstra at Scripps News West Michigan.